1. Field of the Invention
This invention relates generally to the testing of electronic apparatus and more particularly to the testing of the impedances of the interconnect devices by which signals are transferred between electrically coupled system components.
2. Description of the Related Art
As the performance has been improved for data processing systems, the interconnection between the modules, boards, etc of the data processing system has become more critical. The frequencies of the signals in a presently available high performance data processing system are such that the distributed parameters of the connecting cables can be important, requiring that the connecting cables be terminated with the characteristic impedance of the cable (i.e., to minimize signal reflections, etc.). When the properties change for the interconnect apparatus carrying the signals being transferred, either as a result of long term parameter changes or as a result of (relatively rapid) mechanical conditions, the transmission of signals through the interconnect device can be compromised because of a change in the impedance.
In the related art, the testing of the interconnect device has been typically performed with apparatus functioning as an ohmmeter. The only parameter considered important has been the continuity of the electrical connection. However, as described above, the actual value of the impedance of the contact has become important for system operation. In addition, momentary changes in the impedance, which can be produced as a result of mechanical vibration, of the interconnect device can provide an impact on the performance of the data processing system. For testing purposes, the interconnect device can be activated mechanically and intermittent changes in continuity across the interconnect device can be tested. However, the intermittent changes, because of their transient nature, have been difficult to detect and even more difficult to quantify. As will be clear to those skilled in the art, attempts to identify intermittent errors are extremely difficult. An additional problem in the determination of intermittent impedance changes is the verification of the test apparatus used in measuring these changes.
A need has therefore been felt for apparatus and a method that can identify long term and short variations in impedance of interconnect devices transferring signals between system modules.